Occurrence and characteristics of extended-spectrum ß-lactamase-producing Escherichia coli in Swiss and imported retail chicken meat

Objective: The occurrence of extended-spectrum ß-lactamase (ESBL) producing Enterobacterales in food is of concern because of the possibility of transmission of ESBL-producers and/or blaESBL genes to humans. This study aimed to investigate the presence of ESBL-producing Enterobacterales in Swiss and imported retail chicken meat. Methods: A total of 200 samples of different types of Swiss and imported chicken meat obtained at retail level in Switzerland were screened for ESBL-producing Enterobacterales using a selective culture medium. All non-intrinsically resistant isolates were characterised by antimicrobial susceptibility testing (AST), multilocus sequence typing (MLST), and whole genome sequencing (WGS). Results: Eighteen meat samples (9%) yielded a total of 19 ESBL-producing Escherichia coli (ESBL-EC). The proportion of samples containing ESBL-EC was higher in imported meat (14/55; 25%) than in Swiss meat (4/145; 3%). Co-resistance to ciprofloxacin was highly prevalent (18/19, 95%). E. coli sequence types (STs) included ST602, ST744, ST1844, and extraintestinal pathogenic (ExPEC) E. coli ST38. The blaESBL genes comprised blaCTX-M-1 (n=7), blaCTX-M-2 (n=1), blaCTX-M-8 (n=1), blaCTX-M-55 (n=1), blaSHV-12 (n=8), and blaTEM-52B (n=1). They were chromosomally (n=2) encoded or carried on plasmids belonging to IncB/O/K/Z (n=1), IncFII (n=1), IncI1-I(Alpha) (n=9), IncX1 (n=1), and IncX3 (n=5). Many of the plasmids were identical to those detected globally in ESBL-producers associated with broilers. Conclusions: The contamination with ESBL-EC in retail chicken meat in Switzerland is moderate; nevertheless, domestic and imported chicken meat is a potential vehicle for MDR ESBL-EC and for genes conferring resistance to clinically important antimicrobials including 3rd-generation cephalosporins and fluoroquinolones.